[SOLVED] Permanent Manual Postfix configuration help please

One of our clients is going back to Exchange but they want to keep the Zimbr MTA setup as a gateway. I have been able to get the gateway aspect configured manually and tested that it works. However I know that transport_maps parameter is rewritten fresh upon each restart. I need to add another transport_map entry to this line. How do I accomplish this within Zimbra? I looked at zmmta.cf and I have a feeling the answer lies in there but I have no clue how that file works.

Maybe I misled you or I do not fully understand. Postconf just changes the configuration parameter ... I can do that with vi or emacs. The problem is the change is not permanent because the transport_maps parameter in the main.cf config file is regenerated by zmmta.cf when postfix is restarted. How do I make my changes last beyond a restart?